Wave guide switch junction



Jan. 23, 1962 J. s. HOLLIS 3,018,450

WAVE GUIDE SWITCH JUNCTION Filed Oct. 50, 1959 FIG. I

INVENTOR, JOHN s. HOLLIS ATTORNEY leave a coupling gap between the two guides.

United States Patent O Army Filed Oct. 30, 1959, Ser. No. 849,994 6 Claims. (Cl. 333-9) This invention relates generally to low-loss waveguide switches and constitutes an improvement over those disclosed in my US. Patent No. 2,841,770, for Multiple Output Waveguide Switching Systems, granted July 1, 1958, and US. Patent No. 2,826,742 granted to Maurice W. Long and myself, jointly, on March 11, 1958, for Waveguide Ring Switches.

It is an object of this invention to provide a waveguide switch affording a good impedance match and improved wave-transmissionover a broader bandwidth of frequencies than those disclosed in the aforementioned patents.

- It is further an object of this invention to achieve such broad band impedance match, in such a waveguide switch, through simple coupling structure, and without the necessity for special impedance matching means which would involve complicated design and require special adjustment.

While it is common engineering knowledge to scale down an existing long wave device for shorter wave operation, there are several limitations which render unsatisfactory the adaptation of previously known ring switches, both those of the aforementioned patents, and those disclosed by others, from centimeter wavelengths to millimeter wavelengths. It is a further object of this invention to provide a ring switch which avoids these limitations, and which accordingly may be successfully adapted to such shorter wavelengths.

It is further an object of this invention to provide a directional coupler arrangement especially suitable for use in such waveguide switch, which afiords good impedance match over a broad band of frequencies, without the use of special impedance matching means, and which is readily designed for, and satisfactorily operates at millimeter wavelengths.

' It is further an object of this invention to provide such acoupler and waveguide switch which is simply and readily fabricated by conventional manufacturing methods. In accordance with the present invention, my waveguide switch may be comprised of an annulus of waveguide with rectangular cross-section having dimensions appropriate, at the frequency at which itis to be used, for translating energy, as is conventional, in the TE mode. This annulus is split along the mid-lines of the broad walls to form two relatively rotatable portions, inner and outer if the broad walls extend radially, or upper and lower if the broad wall extend axially, whichever may be more convenient in arranging the connections to the equipment with which the switch is to be used. Energy is fed into and out of the annulus through branch arms which are coupled to the narrow wall of the annulus by a form of directional coupler means which I term an Offset Junction.

Such offset junction is formed by two similar waveguides positioned with the respective broad walls of one constituting extensions of the corresponding broad walls of the other, their narrow walls in parallelism, and with each guide intruding into and overlapping the other by half its width. The intruding narrow walls are terminated prior to reaching and overlapping each other, t? This e fectively demarcates a chamber, between the termination of the two abutting guides, having a width of approxi- 3,@l8,45 Patented Jan. 23, 1962 ice mately one and one half normal guide widths, within which chamber higher modes of wave propagation may occur such as will, with proper selection of the gap length, effect a nearly reflectionless transition from the one wave guide to the other over a wide band of frequencies.

For a better understanding of the invention, together with other and further objects thereof, reference is made to the following detailed description, taken in connection with the accompanying drawing, in which:

FIG. 1 is a plan view of one embodiment of the invention, with certain portions broken away to show interior details;

FIG. 2 is a diagram explaining the geometry and operation of the coupling means in FIG. 1; and

FIG. 3 is a perspective view, partly in section, of another embodiment of the invention.

In FIG. 1, reference numeral 16 designates a waveguide annulus of rectangular cross-section, divided into two sections by a gap 11 in each of the broad sidewalls along the respective midlines thereof. These two sections are intended to be so mounted as to be rotatable with respect to each other about a common axis. Thus far, the arrangement is similar to that shown in US. Patent 2,826,- 742, referred to above. The present waveguide ring switch difiers from that one, however in the coupling arrangement provided for coupling energy into and out of the annulus 10. For this purpose, the branch arms 12, 16, 18, 20, and 22, of rectangular waveguide with crosssection of similar dimensions as the annulus 10, are provided. These are coupled to annulus 10, narrow wall to narrow wall, by an offset junction. As shown in FIG. 1, a single branch arm, which may be the input arm, is coupled to the inner section of annulus 10, while four such branch arms 16, 18, 20, 22, which may be output arms, are coupled at uniformly spaced points about the periphery of the outer section of annulus 10. It will be understood, however, that this particular number and arrangement is merely by way of example, and any other number of branch arms as called for by different design details of the switching function might be employed.

The details of the offset junction can best be seen from the couplings of branch arms 12 and 18, where portions of the broad wall of the arms and of the annulus are d picted as having been broken away to reveal the interior of the junction. It will be seen that the branch arm terminates in a portion extending in substantial parallelism with that portion of the annulus 10 to which coupled, this terminal portion or section being so positioned that its broad walls constitute extensions of the broad walls of the annulus 10. It will be also observed that this terminal portion overlies the annulus 10 by half of their widths; hence the name Offset Junction. This is accomplished by providing an aperture 14 in the narrow wall of the annulus 10 at the point where branch arm 12 is to be coupled, and joining the branch arm to the annulus with its nearer wall 13 projecting through the aperture 14 into the annulus 10 to nearly half of its width. It will be apparent from FIG. 1, where the inwardly projecting wall 13 of branch arm 12 is just passing the inwardly projecting wall 17 of the branch arm 16, coupled through the opposite narrow wall of the annulus, that the inwardly projecting narrow walls of the branch arms will fail of reaching the middle of the annular wiveguide by only so much as to allow clearance therebetween as the inner section of the annulus 10 rotates relative to the outer.

The remoter wall of the coupling portion is dimensioned to continue a short distance beyond the aperture 14 in the narrow wall of the annulus 10, and thereby form with narrow wall of 10 a parallel walled chamber, as at 15 and at 19, whose width will be approximately half 3 that of the annulus and branch arm waveguide. The cutoff frequency of such chamber will thus be well above the frequency at which the switch would be used, and any energy which might enter this chamber 15, rather than the annulus, will be rapidly attenuated.

FIG. 2 illustrates the basic geometry of the offset junction employed in the invention. The symbol I represents the input guide of width a, from which energy is to be coupled to the output guide II, also of width at, through a coupling section III of width 2. The thickness of the waveguide wall is designated by d, while the length of the coupling aperture is indicated by b.

The operation and the desirable impedance characteristics of the offset junction are explained by the interaction of energy in the TE mode with energy in the TE mode in the coupling section. That is, energy in the input guide I, propagated in the dominant TE mode will excite also a wave of the TE mode as it passes into the wider coupling section III. The dimensions, particularly e, are such that the TE -mode energy has a lower phase velocity than that of the TE -mode energy. If the length of the coupling section III, that is, the length b of the coupling aperture or slot, is such that the phase difference between the two waves has become 1r, as the entrance to guide II is reached all the energy will be coupled into the guide II, and no reflection will occur because of the junction. While the proper dimension b for this to occur could be approximately computed, because of junction end effects it is usually preferable to determine the appropriate value experimentally. This particular configuration affords especially broadband irnpedance matching by reason of the fortunate occurrence that with this ofiset arrangement the guide wavelength varies faster with frequency for the TE -mode than for the TE -mode. The result is that the phase difference remains approximately 1r over a wide frequency range. With ofiset junctions as shown, I have achieved voltage standing wave ratios of less than 1.1 over a band width exceeding 25 percent.

FIGURE 3 shows another arrangement of a wave guide ring switch embodying my invention, and additionally shows structure particularly adapting it for use in a scanning radiator system such as a Luneberg lens type scanning antenna. In this figure, the wave guide annulus 30, 33 is shown as having the broad dimension of its rectangular cross-section guide in the axial direction, rather than radial as in FIG. 1. Accordingly, the gaps 31 along the mid-lines of the broad walls of the guide divide the annulus into an upper half 30 and a lower half 33. A suitable mounting means 42, shown partly in section, supports the upper half 30 of the annulus in fixed relation to the lens and radiator, of which only the feed are, depicted as an aperture 41 in the support 42, is shown, since the exact details of the Luneberg lens or further structure in the signal path are not material to the instant invention. As seen from the left hand side of FIGURE 3, where a portion of the annulus 30, 33 is represented as having been cut away to show the annulus in cross section, the lower half 33 of the annulus carries a flange 43, which is mounted in ball bearings 44 to permit lower half 33 to rotate relative both to the upper half and to the feed are 41. The internal periphery of the flange 43 may be formed into gear teeth as shown at 45, adapted to be engaged by a motor driven pinion or other suitable drive means, not shown.

Radio waves to be scanned along the length of the feed are 41, shown in cross section in FIGURE 3, are coupled into the fixed upper half 30 of the annulus from a branch arm 32 through an offset coupler similar to those in FIGURE 1, at a point opposite one end of the feed arc. The wave is then coupled out of the annulus and scanned along the feed are 41, as lower half 33 rotates, by successive ones of the several identical coupling sections 34, 36, 40 uniformly spaced along the narrow face of the lower half 33. Lower half 33 has propriate length to pass been depicted with a portion of its broad wall cut away 37, to show the internal structure of these identical couplers. As in FIGURE 1, the coupling portion of the several branch arms 32, 34, 36, and 40, each of wave guide of rectangular cross section of similar dimensions as the annulus, comprises a portion extending in substantial parallelism with the annulus at the region in which coupled, intruding into the annulus to a depth equal to half their widths, and so positioned that their broad walls constitute continuations of the broad walls of the annulus. While arm 32 is depicted with a fractured end, indicating indefinite extension to whatever source desired, output arms 34, 36, 40 are cut to apalong the lips of feed arc 41 as lower half 33 rotates. As in FIGUREI, the nearer wall suchv as 38 of arm 36, passes through an aperture in the narrow wall of the annulus and penetrates to substantially half the depth of the wave guide annulus 30, 33, lacking such by only enough to allow sufficient clearance for couplers on opposite sides of the annulus to pass each other as the lower half rotates. The remoter wall of the branch arm extends beyond the aperture to form with the narrow wall of the annulus a parallel walled chamber of half the width of the wave guide, as at 39, in like manner as in FIGURE 1.

It will be seen from the foregoing that with this invention I have provided a ring switch wherein the gap between the relatively rotatable sections is along the mid line of the broad wall of the guide, as it is in the ring switches in the above referred to patents, as compared to other known ring switches with more complicated coupling arrangements, which require splitting the guide at the corners. As pointed out in Patent No. 2,826,742, referred to above, splitting the guide centrally interrupts a minimum of surface current in the guide walls, and occasions the least radiation loss. This becomes even more serious at higher frequencies where the path along the split guide becomes a larger number of wavelengths of the propa gated energy. So locating the gap avoids the necessity for chokes to prevent such energy loss, which chokes if they were necessary, would entail complications in design for higher frequencies. With the coupling arrangements shown in the aforementioned patents, the losses at the gap occur largely in the regions where the branch arms join the annulus. In the present arrangement, as explained above, the energy in the transition coupling portion between branch arm and annulus is partly in the TE mode as well as the TE mode; however, for the TE mode with the dimensions described, the gap is also at nearly, while not exactly, the position in the broad walls which would interrupt a minimum of surface current. Thus, not only is the broadband impedance match improved through the use of the offset junction, but losses from the gap in the region of inbranching are reduced.

Moreover, it will be seen that the instant coupler achieves the desired broad band operation with utmost simplicity in structure; no special matching means, such as irises or tuning pins, which are inherently narrow band in frequency response, and which raise difiiculties in scaling down to shorter wavelengths, need be used to achieve the desired characteristics.

While I have described preferred embodiments of the invention, numerous changes may be made without departing from the invention, and it is aimed in the appended claims to cover all such changes which fall within the scope of the invention.

I claim:

1. A waveguide coupling member comprising a first waveguide of rectangular cross-section having a coupling aperture in one narrow wall thereof, an inbranching valve wave guide of rectangular cross-section of like dimensions as said first waveguide cross-section having a terminal coupling section of one half normal width extending in substantial parallelism with said first Waveguide alongsaid apertured narrow wall with the respective broad faces of said terminal section and said first waveguide substantially coplanar, and forming along said aperture an enlargement of said first waveguide into a coupling chamber having a uniform width approximately one and one half times the width of said waveguides. I

2. A waveguide junction and coupling means comprising a first waveguide member of rectangular cross-section, said member being divided into two halves by a gap along each midline of each of the two broad faces of said member, means mounting said halves to be moveable relative to each other along the direction in which said member extends, an input arm afiixed to one of said halves and an output arm affixed to the other of said halves, each of said arms comprising a waveguide section of rectangular cross-section of like dimensions as that of said member and including a terminal coupling section extending in parallelism with said member so positioned that its broad faces approximate extensions of the broad faces of said member, said terminal coupling section penetrating through an aperture in the narrow wall of said member to a depth equal to one half the breadth of said waveguides.

3. A waveguide ring switch junction comprising a rectangular cross-section waveguide annulus, said annulus being divided into two halves by gaps along the midlines of each of the broad faces of said guide, means mounting one of said halves for rotation about the axis of said annulus relative to said other half, an input arm waveguide of rectangular cross-section of like dimensions as said waveguide annulus coupled into one of said halves, a plurality of output waveguide arms, each of rectangular cross-section of like dimensions as said waveguide annulus and each coupled at a diiferent point around the other of said halves, each of said couplings comprising a terminal section of the respective input or output waveguide arm extending in substantial parallelism with the portion of the annulus to which it is coupled and its broad faces positioned to approximate extensions of the broad faces of the waveguide of said annulus, said terminal section penetrating through an aperture in the narrow wall of the annulus at the point at which it is coupled to a depth equal to one half of the breadth of said waveguides.

4. A waveguide coupling comprising first and second rectangular cross-section waveguide members, having like cross-section dimensions, and interconnecting means between said members for converting TE mode energy propagated in said first member into a combination of TE and TE mode propagated energy, delaying the TE mode propagated energy relative to TE propagated energy to reverse their respective phases, and recombining said energy in each of said modes to produce energy in the TE mode propagated along the axial direction of said second member to thereby couple energy from said first to said second member, said interconnecting means comprising a chamber having a pair of opposing walls with substantially uniform spacing therebetween of approximately one and one half times the wide dimensions of said members, and one of said walls constituting a uniform continuation of one narrow wall of said first memher.

5. A waveguide coupling member comprising a first waveguide of rectangular cross-section having an aperture in one narrow wall thereof and a coupling section afiixed to said apertured wall, said coupling section comprising an inbranching waveguide arm of rectangular cross-section of like dimensions as that of the said first waveguide terminating in a portion of approximately half normal width extending in substantial parallelism with said first waveguide and forming along said aperture an enlargement of said first waveguide into a coupling chamber of uniform width approximately one and one half times that of said waveguides, the nearer narrow wall of said waveguide arm projecting through said aperture in the narrow wall of said first waveguide and penetrating thereinto approximately half the breadth thereof, the farther narrow wall of said arm continuing beyond said aperture to form with said narrow wall of said first waveguide a parallel walled chamber of half the breadth of said waveguides.

6. A waveguide switching arrangement comprising a main waveguide of rectangular cross-section in the form of an annulus, said waveguide being split at the center of the wide wall to form two relatively-rotatable, complementary sections each of which contains one of the 0pposed narrow walls of the waveguide, at least one branch waveguide of rectangular cross-section with like dimensions as that of the main waveguide connected to each of said sections at the narrow wall thereof, said branch waveguides each terminating in a portion in substantial parallelism with said first waveguide, the nearer wall of said branch waveguide projecting through an aperture in the narrow wall of said main waveguide to which said branch is connected, and penetrating thereinto approximately half the breadths thereof, as parallelism is attained, the farther narrow wall of said branch continuing beyond said aperture to form with said narrow wall of said main waveguide a parallel walled chamber of half the breadth of said waveguides.

References Cited in the file of this patent UNITED STATES PATENTS 2,751,556 Tomiyasu June 19, 1956 2,826,742 Hollis Mar. 11, 1958 2,840,787 Adcock June 24, 1958 

